Manufacture of containers for compressed gases



Nov. 20, 1928,

H. E. STURCKE MANUFACTURE OF CONTAINERS FOR COMPRESSED GASES Filed May s, 1924 SH01 wmf Patentanw.)20,1928.

rss- PATENT ferri-cs.

' HERMAN E.'S'IncxE, or Poner oRANGE, ELoRInA, AsSIGNoR 'ro WILLIAM wnAR'roN, i

an. a coMrANY, .I NconronAfrE ror 1-ENNSYLVAJIIA.`

n, or EASTON; PENNSYLVANIA; A ooEronA'rIoN IIANUFACTUEE or coN'rAINEnS Iron ooMrnEssEn GASES.

` Application filed May 8,

The manufacture offmetal containersfor compressed gases and thelike, and particu.-

'larly thetestingofthecontainers, must 'conform to'specifications and-regulations of the 5 Interstate Commerce Commission. The test l is 4a rigorous one andnot only lare there many f wasters becauseof'failure to meet y the test requirements, but Containers which fulfill such requirements maybe so severely strained' thereby vas to develop potential weaknesses 4which may manifest themselves disastrously.

at any time, thus m With the view of correcting'this evil, some -15 manufacturers, Iabout ten or twelve years ago,

instituted severeheat treatment of .the steel as; a preliminary, step inthe manufacture.

The purpose of this .wastoj produce 'steel of very high elastic limit and containers of comparativelythin wallsand light weight, The

heat 'treatmentv consisted in heating the container' to a temperature of about 1650 degrees F., then quenchingfra few minutes in water heated toaboutldegreesF., or in a corre- .sponding oil bath',^f0llow ed`by' annealing at about 1200 degreesF." It has lbeen d emon` strated that some containers manufactured in this way are dangerously hard;` that the steel lacks uniformity. of quality even as to dif-4 ferent sections of onecontainer. *Also, that aking the containers "unf .the annealing operation fails to'sutficiently'A 1 remove thel heat stresses set up by the quench- "ing. The stress straindiagram of this steel resembles that of cast steel. Many containers operation, the bottoms cracking off. There is no' assuranceY that 4finished containers are free from incipient crackscaused by quenching and 'not removed by annealing and not revealed by pressure test. In the average c ontainer for compressed 'gases the longitudinal stress is less than one-quarterofthe circumfer-y i ential stress. A container may therefore have cracks running circumferentially` through more thanhalf the wall thickness without being materially affected by the pressure test. It is exceedingly difficult to control the heat treatmentso that the containers will not -turn out too'ihard. For instance, containers supposed to withstand atest pressure of 3300 pounds, and not much more, have'been foundto resist pressures of 4100 pounds, and-more, without being stressed beyond the plastic point or the least stress intensity causing plas# crack'during or shortly after the quenchingy 1924. `semi Np. 711,877.

tic flow. Suchjcontainers' obviously are too hard, toughness and ductility -havingbeen sac'zrificedforv an unnecessarilyhigh elastic limit; f f 'f Beca-use ofthe defects, disadvantages, unl certainties and vproblems noted, there is a growing"sentiment against heat treated conta1ners, -and personal observation,investigation and extended experimentation h'aveconvinced me ythat heattreatment is undesirable I and-unsuited for gas containers.

- My invention, therefore, has` for its princi- 'pal objects, the production of containers for .compressed gases unweakened by heat treatment; to provide areliable and economical method' of producing gas containers having 70 desirable properties of strength and toughi ness, 'a' suhciently' high elastic liniit`wl1ich,'f for the sake .of accuracy, I prefer to call the A.

plastic point and which shall be sufficiently d uctile forspeciiied test requirements; tofprovide a gascontainer lWhereofthe qualitiesof strength and ductilityare substantially bal- .ance'd; and to-provide for giving the con--l tainer acold pass without affecting more than the very top surface. Other objects and features oftheinvention will'be discussed in the course of the detailed description' and the invention will finally be-defined inthe claims hereto appended.

In the accompanying drawing,

' Figure l is a chart or diagram ofthe steps -emcployed inthe practice lof my invention, an

Figures 2,3, 4 and 5 are gra hic views of cylinders of the quenched type, s lowing average conditions of fracture under test-orA in According to my invention, I .startthe manufacture of containers with a comparaL tively softfsteel free of heat stresses and mechanical stresses. The containers may be formed in any usu'al'manner, as by piercing or drawing or both. I then remove all incidentalmechanical stresses by thorough an,- i healing. The effect of this is to'lea-ve the steel 100 soft and ductil'e. Hence. there is -no chance for lack 'of uniformity'of quality, no chance for incipient-cracks and no chance for ex-4 cessive hardness. @The soft steel containers are ,subjected vto predetermined interior pressure which stresses them beyond what I termtheplastic point. Mechanical'stresses are thereby set 1up in the container walls, but not to an un-.

necessarily high degree. If the specified test pressure for a certainv class of containers be, for example, 3,0100 pounds, it is not necessary or advisable to use a stretch pressure of more than 8,150 pounds or thereabout. I have shown'in the Bulletin of the'Compressed Gas volume of a container, its efficient (average) wall thickness, the internal pressure and volume increase. I have likewise shown that if a test pressure-is. applied with reasonable speed to a' container, and further pressure i supply is cut off, the test pressure applied may remain constant, thereby proving that the container has not beenstressed beyond the plastic point. If, however, the applied test pressure recedes (not due to leaks or temperature changes) the extent of the recession gives a measure for the permanent non-elastic` condition of the container. lf, therefore, the test pressure is applied with reasonable speed and further pressure supply cut off as soon as the maximum test pressure Vhas been reached, the extent of the test pressure recession gives a close indicationvwhether or not the special container under test is in proper condition to 4be stretched .byAv the predetermined stretch pressure. Excessivev pressure recession indicates that the efficient wall-thickness in general is not as great as required or that the container has local defects, making it unfit for the stretch pressure intended. In this manner containers weakfor any` cause are eliminated previous to the completion of manufacture. ln other words, the preliminary pressure test decides what containers may be safely subjected to the predetermined stretch test without risking unduly hardening them. The preliminary test does not indicate that the container could not be subjected to the stretch pressure and then finally stand the'required test pressure, it is simply a check to sort out vsuchcontainers which if subjected to the stretch pressure would turn out harder thanintended, less tough and less 'ductile If the preliminary pressure test does not show'excessive pressure'v recession, the full stretch pressurel is turned on again and maintained for a brief `period to stretch the container as much as possible under the-applied pressure@ Assuming that the containers have been stretchedto the permissible predetermined limit, the next step is to remove the mechanical stresses or fatigues of the metal.

l have ascertained that this fatigue will disappear if the container is allowed to remain at rest for a time interval, depending upon the stress previously applied and the volume and form of the container, varying -from a few days to a few'weeks. lf it does not interfere with the Vother .operations it will therefore be suflicient to allow the container to remainat rest for the required period in order to remove the fatigue. If, after the rest period, the container 'is subjected to a test pressure of 3,000 pounds, it will be found to stand this test pressure without showing any `or more than a negligible permanent expansion. The test pressure may be raised to 3,150 pounds, the Vpreviously applied stretch pressure, without `showing more than a negligible permanent expansion. F nrt-hermore, and this is very important, the total expansion of the container will now be pro portionate t0 the pressure and entirely elastic; the pressure expansion diagram will be a straight line,proving absence of fatigue or mechanical'stresses. The container has been strengthened to stand the required maximum test pressure with a minimum of loss in toughness, ductility and shock resisting ability.

The rest period treatment may interfere with the other manufacturing operations or yit may be desirable to put the containers. `through 1n a continuous manufacturing process. In this event the. fatigue may be promptly removed by heating the container to a temperature which need not, but may exceed 212 degrees F. Any temperature be-A tween 212 degrees F. and ordinary annealing heat will remove the fatigue in a few minutes. (See J. Muirs Experiments, Encyclopedia Britannica, 11th edition, volume 25, page 1014.) Even at a temperature below2l2 degrecs F; the fatigueis removed in a short time. While, for my invention, it is' not necessary to employ a temperature much above 212 degrees F., itis evident that the fatigue 'rel,moval could be effected, say at 300 degrees F. with superheated steam. In short, while it is a merit of the invention that the fatigue removal'f'can be accomplished at a temperature of substantially 212 degrees F., more or less, l do not restrict myself to such, but may rangebetween 212 degrees F. and 800 degrees, F. v

Containersv produced by piercing or drawing ordinarily present a very rough surface including longitudinal marks, ridges and depressions. Containers made according to -my invention can be given a final cold pass by pressing them through an appropriate draw ring unheated, or only slightly heated.` This has the desired smoothing effect, but sets up mechanical stresses near the surface. These can be largely removed by an additional heating at a temperature not exceeding 800 degrees F. Nevertheless, the surface will remain slightly harder vthan the inner portions of the container walls, but the surface will be much less aected bycorrosion and will ordinarily retain its smoothness for many years.

Having described the nature and o bjects 'of the invention, I claim:

1. In the manufacture of containers for compressed gases, the method-which consists.

informing them from comparatively soft steel substantially devoid of heat and mechanical stresses, annealing them, subjecting the containers tointernally applied pressure corresponding to the ultimate test pressure,

and removing the mechanical stresses set up thereby.

2.In the manufacture of containers for compressedgases, the method which consists in forming them from comparatively soft steel substantially devoid of heat and mechanical stresses, annealing` the containers,l

stretching them beyond the plastic point, and removing mechanical stresses or fatigue by heating the containers at a temperature below such as is calculated to produce any reduction of the elastic limit.

3. In the manufacture of containers fori com ressed gases, the method which -consists in orming them from comparatively soft steel substantially devoid of heat and mechanical stresses, annealing them, `applying a stretch pressure, and removing the fatigue induced thereby by heating the stretched containers to a temperature vot 212 degrees F., more or less.l -v

4. In the manufacture of containers for compressed gases, the method which consists in forming them from comparatively soft steel substantially devoid of heat and mel-` chanical stresses, annealing them, subjecting the annealed containers to predetermined stretch pressure, and removing mechanical stresses caused thereby by heating the stretched containers, for a short period, to a temperature ranging from substantially 21,2l

degrees F. to 800 degrees F.

5. In the' manufacture of containers forv compressed gases, the method which. consists in formin them from comparatively soft steel substantially devoid of heat and mechanical stresses, annealing them, subjectihg the annealed containers to predetermined stretch pressure, removing thefatigue, and hardening the external skin of the containers.

6. In the manufacture of containers for compressed gases, that improvement which consists in stretching a container softer than required to stand the prescribed test pressure,

`HERMAN E. s'racKE 

